This block was donated for review by jb1 (aka Josh Bender) at c5extras.com. He is also the creator of such fine blocks as: Round Corners on Anything, Parent Link and the perennial favorite, Cu3er Slideshow. You can see reviews on all these blocks here and purchase them in the marketplace.
The YouTube Pro block provides a clean interface and standards compliant html for a truly professional look. Setting the width of the video is required for the block to display. Running more than one instance per page is no problem.
Below: the concrete5 core YouTube block provides basic YouTube embedding. The actual url is not wrapped in a script so it is parsed as html by the w3c validator. This yields errors that may be important to some users.
The YouTube Pro blocks simple interface for both edit and add. If you want the video to fill your column you have to enter the number of pixels wide. The height is automatically computed.